


The Cardinal Rule

by castielrisingabove



Category: Supernatural
Genre: Angel Dean Winchester, Destiel - Freeform, Fallen Castiel, First Kiss, Fluff and Angst, Gen, Human Castiel, M/M, angel grace
Language: English
Status: Completed
Published: 2017-02-06
Updated: 2017-02-06
Packaged: 2018-09-22 11:38:55
Rating: General Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 2,687
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/9606107
Author URL: https://archiveofourown.org/users/castielrisingabove/pseuds/castielrisingabove
Summary: Angels aren't supposed to become romantically involved with humans. Only when Castiel at last strikes up a relationship with Dean Winchester does he learn why.





	

_**cardinal** - **rule**. Noun. (plural **cardinal rules** ) A fundamental **rule** , upon which other matters hinge._

 

Even as a rebel, even tearing apart the pre-written script and setting out in his own free will, Castiel had followed the one cardinal rule of angels: never get romantically involved with a human.

Of course, the reasoning for the cardinal rule had constantly been disputed. Naomi used to tell him that the humans corrupted angels. Anna had believed, before cutting out her own grace, that it was the other way around, with angels corrupting humans. Uriel thought of humans as little more than mud-monkeys capable of basic thought, Balthazar found their miniscule time spans not worth investing the effort, Hannah feared angels would accidentally squish them.

It was agreed among all, of course, that romance begat the possibility of a nephilim, which was universally thought to be a danger.

So, despite his growing feelings for Dean Winchester, Castiel had managed to resist them. This rule, this strange cardinal rule, wasn’t worth breaking. At least, he thought so up until Dean almost died saving them from Amara. It was one near-death too many, as far as Castiel was concerned, and he’d kissed Dean without thinking.

And, in a miracle even more unbelievable than his survival, Dean kissed back.

Transitioning from ‘brothers’ to ‘lovers’ had been surprisingly easy. Dean had moved Cas’ few belongings into his bedroom and they’d swapped eager kisses, bodies sunk deep into Dean’s memory foam mattress. Sam had complained about the noise, but in a tone that seemed to imply he didn’t really mind. In fact, Sam seemed oddly pleased and unsurprised about the whole ordeal.

What followed could only be described as domestic bliss.

Castiel surprised Dean with breakfast. With wildflowers he’d found on the side of the road. With a soft yellow hat he’d learned to knit just to keep Dean’s ears warm. Dean, in turn, surprised Cas with mixtapes, with honey from a roadside stand, with endearing sticky notes tacked all over their motel room for Castiel to read at night.

Though, if he was being truthful, Castiel could rarely stay awake all night.

He played it off as wanting to be close to Dean, mumbling sweet nothings about Dean’s intoxicating scent and his soft skin. And of course, all those reasons were equally important as to why he started spending nights in bed, instead of watching over Dean, so Dean did not need to know that Cas was truly sleeping alongside him.

Similarly, Cas eating food soon was more than simply “sharing in the relationship.” Dean was thrilled, of course, to be able to feed Cas all of his favorite foods. And while it was slightly worrisome that his stomach growled if he did not consume food regularly, it  _ was _ nice to be able to taste again. And even nicer having Dean’s fingers to his lips asking him to sample the cherry pie he was baking.

So he was becoming more human? Big deal. He’d been falling anyway. His grace had been waning as it was, it had only been a matter of time before it ran out. And what better way than this? Than gloriously intertwined in the arms of a man he adored above all others in creation? Surely the Winchesters would agree it was worth it.

Still, there was something shameful about admitting it. Dean would likely blame himself, after all, so Castiel didn’t say anything. 

Cas wasn’t the only one who had changed since they’d gotten together, though. Dean bragged about how his benching limit had increased. His instincts on hunts were sharper than they’d ever been. He’d attributed it to being in love with the greatest guy on Earth and Castiel, still high on the glorious feeling of being in love, didn’t question further.

Dean became neater, too, much to Sam’s enjoyment. He stopped playing his music so loud and even started eating more of Sam’s rabbit food. When Cas had asked Sam about the seemingly mystifying changes, Sam had merely grinned.

“It happens, when two people are in love. You bring out the best in each other,” he said with a shrug, “So I guess I’ve got you to thank for the more frequent stops at Whole Foods.” He’d ruffled Cas’ hair and given him a hug. Sam seemed happier these days. They all did.

Everything was perfect. Until suddenly it wasn’t.

Dean stopped eating. Insisted it slowed him down.

Castiel cried so hard after losing a vic on a hunt that he couldn’t see.

Dean constantly hit every mark with perfection while Castiel began struggling in even a basic fight.

The worst of the changes, though, was when Cas collapsed on a hunt after being badly wounded. He was already ashamed by the sign of weakness, nursing a solid guilt for throwing off their plan, and in immense pain from a gash in his side. Dean, rather than tending to his injuries with care, glared at him and informed him he’d compromised the mission. Sam had to help Cas get to the car and even had to call Dean when he discovered his brother had left without them. It was painful and bewildering, Dean’s reaction seemed so alien.

They still shared a bed, though Cas swore Dean only stayed out of duty. Physical affection, on the rare occasions it happened, was stiff. Mechanical. Nothing like the lovely sun-soaked afternoons they’d spent together months before.

Sam tried to reason with Dean, tried to get him to talk to Cas, but Dean refused. Promised they were fine. It wasn’t until one night, when Cas opened his eyes in the darkness, that he saw it. Grace. Shining ever so faintly from under  _ Dean’s _ skin. Castiel touched his shoulder, probing to discover who the grace belonged to and was sent reeling.

The grace was his.

_ The cardinal rule _ .

With every moment Castiel was growing more human, Dean was growing more angelic. 

In a panic, Cas stumbled out of bed, sending a frantic prayer to the only angel he knew who might have an answer. Benjamin had cared for his vessel, had spent time as an angel among humans for decades. 

To his relief, Benjamin arrived swiftly. They’d warmed to Castiel’s case, but recoiled as they surveyed the sleeping Dean, tugging Castiel into a nearby bathroom.

“ _ You’ve ruined him!” _ Benjamin hissed, fingers clenching into Cas’ arm so hard they bruised. “ _ Corrupted his very soul! _ ”

Tears sprung to Cas’ eyes with ease. 

“ _ How could you have forgotten the cardinal law? _ ”

“Benjamin, please. I beg you. There has to be something that can be done. You...you know what it’s like to love a human…”

Benjamin released Castiel slowly, biting their lip. “ _ I loved a human, but I never laid with them. I never let my grace corrupt them _ .”

“I didn’t know--”

“That doesn’t change the fact it’s happened.”

“Can it be stopped?”

Benjamin shrugged. “The moment your final bit of grace slips from your body to his, the ritual will be forever sealed. Your Dean will have most of the powers of Heaven at his fingertips, if he so desires.”

Castiel had to bite down on his lip to keep from sobbing. Had to clench his fists to keep his fingers from trembling. Some human reactions still took getting used to and he hated not being able to control them with ease. Especially around Benjamin (no, if he was being honest, especially around Dean). Slowly, Cas exhaled a shaky breath. “What if we cut out my remaining grace?”

“Aside from the possibility of your death?” Benjamin paused, thoughtful. “It has never been done before, but...it’s possible without the constant surges of power, the grace will eventually drain from Dean’s system as well.”

“It’s worth it.”

“Just like that? The Castiel I knew would never have been so hasty.”

Cas smiled sadly. “The Castiel you knew wasn’t mostly human, either.”

To his surprise, Benjamin smiled too. “I think I like this Castiel more.”

“You’re one of the few who believes so.”

Benjamin reached out to clasp Castiel’s shoulder. It was a comforting gesture. It was true, if the angels did not like Castiel before, they would hate what he’d become. Fallen, weakened, human. But Benjamin, they saw the merit in humanity in ways few angels could.

Benjamin grimaced apologetically. “This will hurt.”

“I know.”

“I’m sorry.”

It was Cas’ scream that woke Sam. It woke Dean too, of course, who’d barrelled into the bathroom with an angel blade drawn, but he’d left as soon as he’d ascertained there was no threat. (Benjamin, of course, had vanished after the deed was done, lingering only briefly to heal the gash across Castiel’s neck.) Sam was the one who had to wipe the blood from Cas’ throat and listen to the wobbling apologies about how Cas had corrupted his brother.

“He wanted you,” Sam whispered gently, wiping the blood from Cas’ bobbing adam’s apple, “You didn’t know this would happen.”

“I should have! There was th-the rule!” Cas whimpered. He felt incredibly guilty, being tended to by Sam like this, but he was too exhausted to move. There hadn’t been much grace left to remove, but the shift to being fully human was still noticeable.

“You really think Dean would have listened to an angel rule?” Sam asked wryly.

“H-he might not ever be the same! He might n-not ever be D-D-Dean!” Clearly Sam was not grasping the full magnitude of the situation. Of all the times Castiel had ever screwed up, this was on par with tearing down Sam’s wall. Utterly selfish on his part, utterly detrimental to a Winchester and, as far as Cas was concerned, utterly unforgivable.

But Sam had always been a kind soul, and forgiveness seemed to be something he did as easily as breathing. Sam smiled, ruffling Cas’ hair, pulling him into a hug to repeat the same words he’d spoken months earlier: “You bring out the best in each other.”

So that’s exactly what Cas tried to do.

It wasn’t easy. Castiel would go out of his way to tell Dean he loved him. On hunts he would compliment his physical prowess, at home he’d mention Dean’s care for Sam, or his taste in music. The bedroom, of course, was where Castiel would break, choking out tearful  _ I love yous _ to a stone-faced Dean. He was always stone-faced, of course. The words of affection, once cherished, meant nothing.

Cas would also tend to Dean’s wounds. Dean, of course, insisted they did not hurt. And perhaps, given the grace in his system, he was right. Still, Castiel would clean the wound carefully, fingertips shaking as he ensured Dean was in good conditions before moving onto the stitching and bandaging. This was still something Castiel was out of practice doing. Before, when Dean was...when he was himself, soft kisses and gentle words of encouragement kept Cas’ spirits up as he apologized over and over for doing a terrible job healing him. Now it was just Cas’ apologies filling the otherwise silent room.

In some desperation, Castiel blasted the mixtapes Dean made him. (Dean complained, informing Castiel the noise was too loud.) He and Sam ordered Dean salads to try to provoke him (Dean shrugged, informing them he didn’t have much of an appetite anyway). Castiel had even learned how to bake pies, clinging to the fantasy that one day, the smell of his favorite dessert and the sight of the man he used to call his sunshine would bring back the Dean they knew and loved. (Dean had merely been annoyed that Castiel wasn’t making himself useful.)

Every day, Cas would try to bring him back, and every night, he’d lay beside Dean, taking note of the fading grace (and it was fading, Dean was glowing less and less each night) and wondering if the changes brought to Dean were permanent. Wondering if his love had truly corrupted the man he adored more than life itself.

Cas would have given up entirely, except for the fact that despite how little Dean seemed to care, he always stayed. He always returned to Cas’ side after a fight, always sat by Castiel during meals, always shared a bed at night. Cas had tried, of course, to get him to stop, but whenever he asked why Dean stayed, Dean shrugged and replied, “You’re my angel. I can’t leave you.”

It wasn’t much, Dean still rarely provided anything more than his  presence, but it was enough to keep Cas holding on.

\---

Several months passed. Castiel still baked Dean pies. One every Sunday. This particular Sunday’s was apple, he’d even branched out and added caramel to the filling. By now, of course, the pies were mostly for his and Sam’s enjoyment, but Dean was always present in the kitchen. Just in case. Sam was fetching him now, Dean was no doubt polishing the weapons in the armory again. Cas was humming to himself while he pulled the pie from the oven ( _ Hey Jude _ . One of Dean’s favorites) when--

“Holy shit, that smells  _ awesome! _ ”

Castiel almost dropped the pie, barely managing to slide it onto the counter as he turned to see Dean, grinning at him from the doorway.

“Dean?” Cas gasped, painfully aware of how unnecessary the words sounded and bracing himself for Dean’s scolding. But it didn’t come. Instead.

“Sam’s been talking up your pies like they’re friggin’ salads or something, so I figure, really, it’s my duty to eat most of it before he gets fat.”

“Dean?” this time Cas’ voice was wobbly. On the verge of tears. Was this real? Or was he sleeping again? Castiel had dreamt too many situations where Dean had returned to normal, each one more painful to wake up from than the last. 

Dean’s eyes widened. “Aw, shit. Sammy got like this too. I know I’ve been an ass and I’m sorry--”

Dean was cut off by a tight hug, Cas pressing his face into the nape of his neck. Tears were falling fast now, dripping embarrassingly onto his shirt. And Dean,  _ oh _ , Dean held him close. Rubbed soothing circles on his back like he used to, so many months ago. 

“I wasn’t myself for a while, was I?” Dean whispered.

Cas tried to explain, how it was his fault for selfishly wanting Dean, for subjecting him to the one rule he was not supposed to break, for turning Dean into the very thing he hated but all that came out was a sob.

By now Dean had taken to kissing the tears from Cas’ cheeks--which in turn made Cas cry harder--and Sam had made his way into the kitchen and grown equally misty-eyed. Which meant Dean was pulling them both into a hug, held for far too long to even be considered reasonable until Dean mumbled, “Can we please have some pie now?”

The explanations would come later, of course. The apologies would follow shortly after. But far into the night, full of apple pie and caramel soaked kisses, Dean would answer the question that had plagued Castiel. “I’m glad you did it, y’know,” he whispered. “Broke that angel rule.”

“Dean, we almost lost you.”

Dean shook his head, a gentle smile on his face. “No offense, sunshine, but you never would have lost me. You have always brought me back.”

“I rebelled most of those times. Including this one. Saving you has always been uncertain,” Cas replied sadly. He was so used to Dean rattling off statistics, telling him he’d been too careless, acting not unlike a member of his garrison. But Cas knew the grace had well and truly drained when Dean replied.

“Mmm, I’m dating a rebel,” Dean smirked, kissing Cas again. “I love you, rebel.”

Cas beamed, shyly trying a reference he hoped Dean would understand once again. “I know.”

He wouldn’t have been surprised if Dean’s laughter woke Sam.

Perhaps the angels were right. Loving a human meant corrupting them. It meant corrupting each other. But perhaps Sam was also right. That if the right people loved each other the right way, they’d bring out the best in each other too.

 

**Author's Note:**

> Kudos and comments are always appreciated! Especially if you liked the work. Or you can come flail with me about destiel theories at my tumblr: @castielsunshinegrace


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